Traditional circuit control devices have a component, such as a turnable knob for example, that is physically moved by the operator in order to change an electrical condition in the controlled circuit. Potentiometers, rotary variable resistors and rotary encoders are examples of control devices of this type. Controls which require physical movement of a component by the operator are preferred by many persons and are less prone to erroneous input because of the tactile feedback which the operator receives. Some newer forms of circuit control such as touch screens for example do not provide this kind of feedback.
Conventional controls which have a knob that is turned by the operator are not well adapted for use with some newer types of electronic circuit. The control typically requires calibration marks or other graphics around the perimeter of the knob and additional graphics which identify the function of the control and/or other information pertaining to operation of the control. In the conventional construction a shaft extends through a control panel. The turnable knob is in front of the control panel. Other components of the control device are behind the panel and are interconnected with the knob by the shaft. The graphics are permanently imprinted on the front of the control panel. Fixed graphics of this kind can severely limit the functions of the control device and can cause operator error under certain circumstances. This problem occurs in electronic systems in which a single control device is used for different purposes at different times. For example, a station selector knob of a radio requires one set of graphics when the radio is operating in the AM mode and a different set of graphics when the radio operates in the FM mode. Multiple function controls of this kind are also found in diverse other types of electronic apparatus such as computer alphanumeric keyboards and synthesizer keyboards for example. In many cases the operator must memorize the alternate functions of such controls or consult a chart or resort to such expedients as disposing an overlay on the controls that is imprinted with changed graphics.
Problems of the above described kind can be alleviated by associating an image display screen with the circuit control device to enable display of instantly changeable images on or in the vicinity of the control. Under microprocessor control, graphics for the control device can be caused to change automatically when the function of the control device changes. Under some circumstances this can be beneficial at single function control devices as well as at multiple function controls. For example, the language of the labeling at a circuit control device can be caused to change instantly in response to operation of a language selection key.
Prior rotary knob circuit control devices having an image display which provides instantly changeable graphics have characteristics that can be a source of problems at least under some circumstances. The control device and the image display screen are at different locations on the control panel and the image display area of the screen is bounded by a peripheral region of the display which contains structural framing, seals and other components. The display cannot provide calibration marks around the perimeter of the knob and the sizable spacing between the graphics and the knob complicate the operator's task of associating graphics with the specific controls to which they relate.
Some prior rotary controls of the above described kind have a thicker and bulkier construction then is desirable for some usages such as in constricted locations or where a thin control panel is to be disposed against a wall for far example. Some can be difficult and costly to manufacture particularly if precise control signals and a long operating life are desirable criteria. Others can produce only a very limited variety of different graphics.
Repair or replacement of prior rotary knob control devices requires access to the back of the control panel. This complicates such operations and deters many users of control devices from personally undertaking the repair or replacement.
The present invention is directed to overcoming one or more of the problems discussed above.